For completeness, can you check whether you are actually running out of NPP or not. You can use the Poolmon tool to help with this issue. See: http://www.adopenstatic.com/cs/blogs/ken/archive/2006/07/10/Using-PoolMon-_2800_Pool-Monitor_2900_-to-debug-kernel-memory-leaks.aspx
and
http://blogs.msdn.com/b/amol/archive/2012/02/29/troubleshooting-quot-connections-refused-quot-errors-seen-httperr-logs.aspx
If you are not actually out of non-paged pool, then we may all be barking up the wrong tree. On the other hand, you may have some other app (e.g. in my blog post we can see that a particular AV client was leaking NPP) that is leaking NPP, and even changing http.sys behaviour may not help if NPP is completely exhausted.